Spray-coating apparatus

Abstract

Spray coating apparatus comprises a spray nozzle (2) and a regulation system (16) which limits the high voltage at a high-voltage electrode (10) to a predetermined voltage value. The system also directly measures and limits the electric spray current of the high-voltage electrode (10) to a predetermined current value. The electric spray current is limited by adjusting the high voltage at the high-voltage electrode (10).

What is claimed is:  
     
       1. A spray-coating apparatus, comprising: 
       a spray nozzle for spraying a coating material onto an electrically conductive object to be coated;  
       at least one high-voltage electrode for electrostatically charging the coating material sprayed from said spray nozzle;  
       a high-voltage source for applying a high voltage to said high voltage electrode, the high voltage causing the electrostatically charged coating material to move towards the object to be coated resulting in a spray current; and  
       a regulation system for measuring and regulating the spray current so that the spray current does not exceed a predetermined spray current limiting value, said system being electrically connected to the object to be coated by a return path;  
       wherein said regulation system comprises  
       a spray current measuring circuit installed in the return path for measuring an instant value of the spray current flowing therein; and  
       a control circuit coupled to the spray current measuring circuit for regulating the high voltage applied to said high voltage electrode based on the measured instant value of the spray current;  
       wherein said regulation system further regulates the high voltage applied to said high voltage electrode so that the high voltage does not exceed a predetermined high voltage limiting value;  
       wherein said control circuit comprises  
       a current comparator coupled to the spray current measuring circuit for receiving and comparing the measured instant value of the spray current against the spray current limiting value, and generating a high voltage regulating value based on said spray current value comparison; and  
       a voltage comparator coupled to the spray current comparator for receiving and comparing the high voltage regulating value against the high voltage limiting value, and generating a control voltage based on said high voltage value comparison.  
     
     
       2. The apparatus of  claim 1 , wherein the control voltage is fed to said high voltage source for adjusting the high voltage applied to said high voltage electrode. 
     
     
       3. The apparatus of  claim 2 , wherein said high voltage source has a high voltage part for generating the high voltage to be applied to said high voltage electrode, and a low voltage part for receiving the control voltage and adjusting the high voltage based on the received control voltage. 
     
     
       4. The apparatus of  claim 3 , wherein the low voltage part of said high voltage source comprises an oscillator. 
     
     
       5. The apparatus of  claim 1 , wherein the current comparator is a proportional-integral control. 
     
     
       6. The apparatus of  claim 1 , further comprising a memory for storing the spray current limiting value and the high voltage limiting value, said memory being coupled to the current and voltage comparators for feeding the stored spray current limiting value and high voltage limiting value thereto, respectively.